JPH02121139A - Magneto-optical pickup - Google Patents

Abstract

PURPOSE:To form the above pickup simpler in constitution and smaller in size and to facilitate the position adjustment thereof by providing holograms having polarization characteristics and holograms for error signal detection on the respective end faces of transparent substrates and integrating the substrate. CONSTITUTION:The composite hologram lens 10 has, successively from a half mirror side, a halfwave plate 14, a 1st hologram 11, a 2nd hologram 12, the transparent substrate 15, and a 3rd hologram 13. The 2nd hologram 12 is joined to the half mirror side surface of the substrate 13 and the 3rd hologram 13 is joined to the other surface. The 1st hologram 11 is joined onto the 2nd hologram 12 and the halfwave plate 14 is joined onto the 1st hologram 11. The return light from the recording medium is made incident to the hologram 12 having the polarization characteristics, by which the luminous flux for information signal detection is formed. This luminous flux is made incident to the hologram 13 for error signal detection, by which the luminous flux for error signal detection for at least either of focusing and tracking is formed. The constitution is simplified and miniaturized in this way, and the need for the position adjustment of the holograms is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical pickup using a hologram in an optical system.

[Problems to be solved by conventional techniques and inventions] In recent years, the information-related industry has made remarkable progress, and the amount of information handled has also tended to increase. For this reason, instead of recording or reproducing devices that use conventional magnetic heads to record or reproduce information, it is possible to record information at high density on a recording medium by irradiating a light beam, or to record information on a recording medium at high density. 2. Description of the Related Art Optical information recording and reproducing devices capable of reproducing information recorded at high density at high speed are in demand.

In addition, as a rewritable recording method, the magneto-optical method, which records information on a recording medium depending on the direction of magnetization (upward and downward) and reproduces the information using magneto-optic effects such as the Kerr effect, is attracting attention. There is.

The magneto-optical method requires a magneto-optical pickup that can read the rotation of the plane of polarization. Conventionally, in this magneto-optical pickup, a polarizing beam splitter has been used to separate two orthogonal linearly polarized components.

However, when using a conventional beam splitter,
Since the two divided polarized light components are emitted in directions perpendicular to each other, this has been a factor hindering miniaturization of the pickup.

To deal with this, for example, Japanese Patent Application Laid-Open No. 62-293543
The publication describes a reproduction optical system that separates two orthogonal linearly polarized components using a parallel polarizing beam splitter and a compound lens, and obtains a reproduction signal from the difference in the output of two photodetecting elements that receive the separated eight beams. system is disclosed.

However, since the optical system uses a parallel polarizing beam splitter and a compound lens, there is a problem that the holder for attaching the prism frame and the compound lens is complicated and large.

Furthermore, in another example of the preceding example, a single lens is interposed between the polarizing prism and the photodetecting element in the optical system for detecting the reproduced signal, but in this case, the optical positioning holder is However, there is a problem in that the shape of this holder becomes complicated.

Furthermore, in the prior art example, a mechanism is required to rotate the parallel polarizing prism and the photodetecting element together. This is because the prism is rotated by 45 degrees with respect to the polarization direction of the incident light, and in this case, it is installed at an appropriate position depending on the machining precision, but the prism or the holder that supports the prism is Fine rotation adjustment is required depending on machining accuracy and prism joining accuracy.

Furthermore, recently, in order to make the pickup smaller and lighter, an optical system using a hologram has been proposed. For example, Japanese Patent Application Laid-open No. 63-74149 discloses a pickup that uses a surface relief hologram to separate P-polarized light and S-polarized light, and obtain a reproduced signal from the difference signal.

This prior example discloses an example in which the optical system is integrated with a metal casing, but in this case, accurate position adjustment of the hologram is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magneto-optical pickup that has a simple configuration, allows miniaturization, and facilitates position adjustment.

[Means for Solving the Problems] The magneto-optical pickup of the present invention includes a light beam for detecting information signals in an optical system between a recording medium and a photodetector that detects return light from the recording medium. A hologram having a polarization characteristic to generate a hologram, and an error signal detection hologram to generate a light beam for detecting at least one of focusing and tracking error signals, and the hologram having the polarization characteristic and the error signal detection hologram are integrated by providing them on each end surface of a transparent substrate.

[Function] In the present invention, the return light from the recording medium is incident on a bologram having polarization characteristics to generate a light beam for detecting an information signal, and is also incident on a hologram for detecting an error signal to perform at least focus and tracking. A light beam for detecting one error signal is generated.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 1 to 5 relate to the first embodiment of the present invention.
Does the diagram show the configuration of a magneto-optical pickup? Figure 2 is a side view showing the composite hologram lens and photodetector, Figure 3 is a circuit diagram showing the circuit for detecting information signals, focus, and tracking error signals, and Figure 4 is a diagram showing the circuit for detecting the information signal, focus, and tracking error signal. FIG. 5 is an explanatory diagram showing the manufacturing method of the third hologram.

As shown in FIG. 1, a magneto-optical pickup 1 for recording, reproducing, and erasing information on a magneto-optical recording medium 3 uses a semiconductor laser 2 as a light source.
and the recording medium 3, a collimator lens 4. Half prism 5. An objective lens 6 is provided.

Then, the linearly polarized light (
The light beam (P polarized light) is made into a parallel light beam by a collimator lens 4, passes through a half prism 5, and is focused onto a recording medium 3 by an objective lens 6. Information is recorded on this recording medium 3 by upward magnetization and downward magnetization. Therefore, the plane of polarization of the P-polarized light incident on the recording medium 3 is rotated by the magneto-optic effect (Kerr effect) according to the magnetization direction of the recording medium 3. For example, if the plane of polarization rotates by θ degrees for upward magnetization, the plane of polarization rotates by 1 θ degree for downward magnetization.

The reflected light having the S-polarized component due to the rotation of the plane of polarization becomes parallel light again by the objective lens 6, and is partially reflected by the half prism 5 to form the composite hologram lens 1.
It is set to be incident on 0. Each light beam divided by the composite hologram lens 10 is received by a photodetector group 20, and the output of this photodetector group 20 is input to a detection circuit 30, which outputs an information signal and a focus signal. A tracking error signal is generated.

Incidentally, instead of the half prism 4, a beam splitter may be used which can appropriately set the transmission and reflectance of P-polarized light and S-polarized light.

The composite hologram lens 10 and the photodetector group 20 are
It is constructed as shown in FIG.

That is, this composite hologram lens 10 includes, in order from the half mirror 4 side, a 1/2 wavelength plate 14°, a first hologram 11. Second hologram 12. It has a transparent substrate 15° made of glass or plastic, and a third hologram 13, and a second hologram is provided on the surface of the transparent substrate 13 on the side of the half mirror 4.
The hologram 12 is bonded, and the third hologram 13 is bonded to the other surface. Further, the second hologram 1
A first hologram 11 is bonded onto the top of the second hologram 2, and a 172 wavelength plate 14 is bonded onto the first hologram 11 as necessary.

The azimuth angle of the half-wave plate 14 is set to 22.5° in order to rotate the polarization direction of the incident light by 45°.

The first hologram 11 diffracts the incident parallel light so as to change the polarization direction so that the polarization diffraction efficiency is optimal for the second hologram 12.

The second hologram 12 uses, for example, a surface relief pear hologram having polarization characteristics, and is similar to the first hologram 1.
The light from 1 is separated into transmitted light and diffracted light. The second hologram 12 has, for example, a diffraction efficiency of 85 to 80% for S-polarized light, a transmittance of 15 to 20%, and 100% diffraction for P-polarized light. There is.

The third hologram 13 divides the transmitted light of the second hologram 12 into two semicircular beams, and diffracts the semicircular beams so as to focus them on different focal points. At the position where each semicircular beam is received, there is a photodetector S1. S2 is provided. Note that one photodetector S1
The focal point of the semicircular beam incident on the other photodetector S1 is located at a position farther from the photodetector S1, and the focal point of the semicircular beam incident on the other photodetector S2 is located at a position closer than the photodetector S2, and When in focus, the areas of the semicircular beams projected onto both photodetectors 81 and 82 are made equal.

Further, the third hologram 13 is configured to diffract the diffracted light of the second hologram 12 so as to converge it. A polarizing prism 21 is arranged on the optical path of this diffracted light. This polarizing prism 21 has a polarizing film surface 22 that transmits P-polarized light and reflects S-polarized light, and reflects the reflected S-polarized light on a slope 23 to separate P-polarized light and S-polarized light, and P-polarized light and S-polarized light are emitted in substantially the same direction.

P polarized light and S polarized light separated by the polarizing prism 21,
A photodetector 83, 84 is provided at each light receiving position n.

Further, the photodetector group 20 consisting of the photodetectors S+, 82.83, and S+ is provided on the same substrate 25 and integrated.

Incidentally, even if the photodetector group 2o magnetized in this way and the composite hologram lens 10 are integrated, there is still a problem.

With this configuration, the return light from the recording medium 3 is reduced to 1
The polarization direction is rotated by 45 degrees by the /2 wavelength plate 14, and the first
The polarization direction is changed by the hologram 11 so that the polarization diffraction efficiency is optimal for the second hologram 12, and
The light enters the hologram 12. The transmitted light of this second hologram 12 is split into two semicircular beams, and each semicircular beam is incident on a photodetector 81.82. Focus and tracking error signals are generated from the output signals of the photodetector Sz and 82. Further, the diffracted light of the second hologram 12 is polarized by a polarizing prism 21.
The polarized light and the S-polarized light are separated, and the P-polarized light is received by a photodetector S3, and the S-polarized light is received by a photodetector S4. An information signal is generated from the output signal of this photodetector 83°8+.

The focus and tracking error signals and information signals are detected as follows.

As shown in FIG. 3, the photodetectors S1 and 82 are each composed of two divided photodetectors Su, St2 and S13°S14, and the focus error signal is detected by a subtractor 34 using a double knife. By (Stt+S+a)
It is obtained by calculating -(S12+814).

Tracking error signal detection uses a push-pull method, and when the light beam is moved relative to the track, the two semicircles move in the same direction, so the adder 31 detects the photodetector S11.
．． The output of S12 is added, and the adder 32 adds the output of S12 to S+ of the photodetector.
3. The outputs of St+ are added, and the subtracter 33 adds the outputs of St+ to the adder 31.
It is obtained by calculating the difference between the 32 outputs.

Further, the information signal of the data section is obtained by calculating the difference between the outputs of the photodetectors S3 and $4 in the subtracter 35, and the information signal of the pre-pit section is obtained by the subtractor 35 by calculating the difference between the outputs of the photodetectors S3 and S3.
It is obtained by calculating the sum of the outputs of and 84.

By the way, the first hologram 11 is created as shown in FIG. That is, a plane wave L1 is made perpendicularly incident on the dry plate 11a which becomes the first hologram 11, and another plane wave L2 from the same generation source is made incident at a predetermined angle, and the first hologram 11 is made by double exposure method. is created.

Further, the third hologram 13 is created as shown in FIG. In creating this third hologram 13, it is important to reduce aberrations. 3rd hologram 1
Two plane waves 01.02 having a predetermined inclination are made incident on the dry plate 13a of 3. Further, from the opposite side of the dry plate 13a, plane waves 03 emitted from the same light source as 01.02 are transmitted to fl, f2. The light is made incident on a microlens group 40 consisting of microlenses 41, 42, and 43 having a focal point of f3. Then, plane wave 01 and lens 4
The third hologram 13 is created by each double exposure of the spherical wave from 3, the plane wave 02 and the spherical wave from the lens 41, and the plane wave 02 and the spherical wave from the lens 42. Note that the focal point of each microlens 41, 42, 43 is f2 > f3 >
The relationship is fl. In addition, each micro lens 41
, 42°43, a pinhole 45 is placed at a focal point of 42°43,
The effect of aberrations due to higher-order diffraction is removed.

Such a hologram lens is advantageous in that it can utilize diffraction and can be determined according to the arrangement of the photodetector, and is particularly effective for complex opto-magnetic differential optical systems.

Next, the second hologram 12, which is small and has polarization characteristics in this embodiment, will be explained. In general, the grating pitch depends on the wavelength of light, and in particular, when λ/d (λ: wavelength, d: grating bit) becomes smaller, birefringence occurs, and birefringence tends to increase as the wavelength becomes smaller. be. Furthermore, by selecting an appropriate non-Bragg angle as the incident angle, it is possible to make the diffraction efficiencies of both polarized light perpendicular to the grating grooves and polarized light parallel to the grating grooves large and equal.

In addition, instead of rotating the polarization plane by 45 degrees using the 1/2 wavelength plate 14, the 1/2 wavelength plate 14 is removed and the S
The grating groove of the second hologram 12 is set at 45° with respect to the polarized light component.
By rotating and arranging the second hologram 12 and setting the incident angle to a non-Bragg angle, it is possible to make the diffraction efficiency of polarized light perpendicular to the grating grooves and polarized light parallel to the grating grooves the same. .

In this way, according to this embodiment, the second
Since the hologram 12 and the third hologram 13 for error signal detection are integrated by providing them on each end face of the transparent substrate 15, the configuration is simple and compact, and the positions of both holograms 12 and 13 can be easily adjusted. becomes unnecessary. Furthermore, the holder has a simple cylindrical shape, resulting in a compact, low-cost pickup suitable for mass production.

Also, the second hologram 12. Along with the third hologram 13, the 1/2 wavelength plate 14. By integrating the first hologram 11, the structure can be made simpler and smaller.

Furthermore, by using the composite hologram lens 10 of this embodiment, the photodetector group 20 can be integrated, and rotational adjustment becomes unnecessary.

Furthermore, by integrating the composite hologram lens 10 and the photodetector group 20, it becomes unnecessary to adjust the positions of both.

Also, the first hologram 11 causes the second hologram 12 to
A differential optical system with good diffraction efficiency can be obtained by adjusting the incident angle to obtain the optimum polarization diffraction efficiency.

FIG. 6 is an explanatory diagram showing the configuration of a magneto-optical pickup according to a second embodiment of the present invention.

In this example, recording is performed using a two-wavelength semiconductor laser.

This is an example of a pickup that can be played and erased.

The light beam emitted from the erasing semiconductor laser 51 becomes parallel light by the collimator lens 52, passes through the half prism 53, is reflected by the dichroic mirror 54,
The light returns to the half prism 53 again, a portion of which is reflected, and is focused by the objective lens 6 onto the surface of the magneto-optical recording medium 3. The returned light from the recording medium 3 passes through the objective lens 6, passes through the half prism 53, and is cut by the Dyke O'cum mirror 56, so that it does not enter the photodetector.

On the other hand, the light beam emitted from the recording/reproducing semiconductor laser 57 is turned into parallel light by a collimator lens 58, turned into a circular beam by a shaping prism 59, passes through a dichroic mirror 54, and is partially reflected by a half prism 53. The reflected light is focused onto the surface of the recording medium 3 by the objective lens 6. The return light from the recording medium 3 passes through the objective lens 6, half prism 53, and dichroic mirror 56, passes through the composite hologram lens 10 similar to the first embodiment, and is received by the photodetector group 20. , focus, tracking error signals, and information signals can be obtained.

Other functions and effects of the configuration 1 are the same as those of the first embodiment.

7 and 8 relate to a third embodiment of the present invention, in which FIG. 7 is a side view showing a composite hologram lens and a photodetector, and FIG. 8 is a circuit for detecting information signals, focus, and tracking error signals. FIG.

In this embodiment, the second hologram 12 separates P-polarized light and S-polarized light using transmitted light and diffracted light. The transmitted light of the second hologram 12 is separated by the third hologram 13 into a semicircular beam and two quarter circular beams. The semicircular beam is incident on two divided photodetectors S31 and S32, and each quarter circular beam is incident on photodetectors 833 and 834, respectively.

Focus error signal detection uses the Knifezi method, and at the time of focusing, the semicircular beam is detected by the photodetector ZS3.
When the focus is established between t and S32, and the third surface of the recording medium is closer than the focus of the objective lens, the photodetector S32
A semicircular image is projected onto the top, and conversely, when the third surface of the recording medium is defocused and is farther from the focal point of the objective lens, the photodetector S3
A semicircular image is projected onto 1. Therefore, subtractor 6,2
According to the photodetector S31. A focus error signal is obtained by calculating the output difference in S32.

Further, tracking error signal detection uses a push-pull method, and when a track offset occurs, the photodetector S33. The size of the image of 174 yen in S34 metaphysics becomes asymmetrical. Therefore, by the subtractor 61, the photodetector S
33. It is obtained by calculating the output difference of S3+.

Further, the diffracted light from the second hologram 12 is diffracted by the third hologram 13 and is made to enter the photodetector 6S 3s. Then, the information signal of the data part is sent to the photodetector S31. It is obtained by calculating the difference between the sum of the outputs of S32゜S3a, 8a+ and the output of the photodetector 835, and the information signal of the pre-pit section is sent to the adder 6.
4, the photodetector Sa1. S32, 833. SO and S
It is obtained by calculating the sum of the outputs of 34.

Although a 1/2 wavelength plate is not used in this embodiment, the same effect can be obtained by arranging the relief groove direction of the second hologram 12 at a position rotated by 45 degrees with respect to the P-polarized light of the incident light. Effects can be obtained.

According to this embodiment, compared to the first embodiment, there are fewer photodetectors and there is no polarizing prism 21, so the configuration is simpler and can be made smaller.

Additionally, the light beam for detecting the focus error signal and the light beam for detecting the tracking error signal are separated, and both light beams are received by separate photodetectors, so that the focus and tracking error signals are independent of each other. Since the error signals can be detected immediately, mutual interference between the error signals is eliminated.

Furthermore, the error signal and information signal generation circuits are simpler than those in the first embodiment.

The other functions and effects of the configuration 9 are the same as those of the first embodiment.

9 and 10 relate to the fourth embodiment of the present invention, and FIG.
The figure is a side view showing the composite hologram lens and photodetector.
FIG. 10 is a circuit diagram showing a circuit for detecting information signals, focus, and tracking error signals.

In this embodiment, the second hologram 12 separates the light from the first hologram 11 into transmitted light and diffracted light, but for S-polarized light, the diffraction efficiency is set to 15 to 20%, and the transmittance is set to 15% to 20%. 85 to 80%, and 100% of P-polarized light is transmitted.

The transmitted light of the second hologram 12 is transmitted to the third hologram 1
3 and enters the polarizing prism 21, where the P-polarized light and the S-polarized light are separated, and the P-polarized light is received by the photodetector S3.
The S-polarized light is received by a photodetector S4. Then, as shown in FIG. 10, in the same manner as in the first embodiment, the photodetector S3
．． Information signals of the data section and the prepit section are generated by the output signal of 84.

Further, the diffracted light of the second hologram 12 is divided into two semicircular beams by the third hologram 13, and each semicircular beam is transmitted to the photodetector 31.82 as in the first embodiment.
incident on . Focusing is then performed by the output signal of this photodetector Ss, 82.

Tracking error signals are generated.

The other functions and effects of the configuration 9 are the same as those of the first embodiment.

Note that the present invention is not limited to the above-mentioned embodiments. For example, a hologram having polarization property is not limited to a surface relief type hologram, and a hologram having a polarization property is not limited to a surface relief type hologram. A phase grating hologram that takes advantage of the large change in diffraction efficiency may also be used.

[Effects of the Invention] As explained above, according to the present invention, a hologram having polarization characteristics and a hologram for detecting an error signal are provided on each end face of a transparent substrate and integrated, thereby simplifying the structure of a magneto-optical pickup. This has the effect of making it possible to reduce the size and making position adjustment easier.

[Brief explanation of drawings]

FIGS. 1 to 5 relate to the first embodiment of the present invention.
The figure is an explanatory diagram showing the configuration of the magneto-optical pickup, the second figure is a side view showing the composite hologram lens and the photodetector, and the third figure is an explanatory diagram showing the configuration of the magneto-optical pickup.
The figure is a circuit diagram showing a circuit for detecting information signals and focus and tracking error signals, FIG. 4 is an explanatory diagram showing a method for manufacturing the first hologram, FIG. FIG. 6 is an explanatory diagram showing the configuration of a magneto-optical pickup according to a second embodiment of the present invention, FIGS. 7 and 8 are related to a third embodiment of the present invention, and FIG. 7 shows a composite hologram lens and a photodetector. FIG. 8 is a circuit diagram showing a circuit for detecting information signals, force h, and tracking error signals, FIGS. 9 and 10 relate to the fourth embodiment of the present invention, and FIG. FIG. 10 is a side view without showing the composite hologram lens and photodetector, and a circuit diagram showing a circuit for detecting information signals, focus, and tracking error signals. 1... Magneto-optical pickup 3... Magneto-optical recording medium 10... Composite hologram lens 11... First hologram 12... Second hologram 13... Third hologram 15... Transparent substrate 20 ...Photodetector group 30
...Detection circuit Figure 4 Figure 5'' Masashi Mitsuki Neyama (self-proposal) November 29, 1988 [1 1, Indication of the incident 1988 Special revision application No. 273829 2, Name of the invention Optical magnetism Pickup 3: Relationship with the person making the amendment Patent applicant Address: 2-43-2 Hatagaya, Shibuya-ku, Tokyo (037) Representative of Olympus Optical Industry Co., Ltd.
Satoshi Yama, Department 4, Agent/Address: 7-4-4-6 Nishi-Shinjuku, Shinjuku-ku, Tokyo, “Claims” and “Detailed Description of the Invention” column 1 of the specification subject to amendment, The scope of patent claims will be amended as follows. ``A photodetector that detects the magneto-optical recording medium and the return light from the magneto-optical recording medium is installed in the magneto-optical pickup which generates an information signal by using the polarization information of the return light from the magneto-optical recording medium. A bologram having polarization characteristics that generates a light beam for detecting information signals and a hologram for error signal detection that generates a light beam for detecting at least one of focusing and tracking error signals are provided in the optical system between the , a magneto-optical pickup characterized in that the hologram for controlling the polarization characteristic and the hologram for detecting the error signal are integrated by providing them on each end surface of a transparent substrate.'' 2. Box in the specification. In the 10th and 11th lines of page 2, "...recording medium..." has been corrected to "...magneto-optical recording medium...". 3. In the 14th line of box 6 of the specification, [...Recording medium...] has been corrected to "...Magneto-optical recording medium...". 4. In the 20th line of box 6 of the statement, correct [...recording medium...] to "...magneto-optical recording medium...". 5. Correct "...Recording medium..." in the first line of page 7 of the statement box to "...Magneto-optical recording medium..." 6. In the 3rd line of page 7 of the specification Yamanaka, “The above-mentioned recording medium
..." was corrected to "the magneto-optical recording medium...". 7. In the 3rd or 4th line of the 7th page of Yamanaka details,
...Recording medium..." is changed to "...Magneto-optical recording medium...
・Corrected to ``. 8. “Half mirror 4” on the 4th line of box 8 of the statement
"Side..." will be corrected to "Half mirror 5 side...". 9. In box 8 of the statement, line 7 or line 8, "
..." on the half mirror 4 side of the transparent substrate 13" is replaced with "..."
...on the half mirror 5 side of the transparent substrate 15..." first. 10. Lines 16 to 17 of page 10 of the specification cylinder
Delete the line ``In addition, it may be converted into a stock like this...''. 11. Correct "...Recording medium..." in line 18 on page 10 of the specification to [...Magneto-optical recording medium...].

Claims (1)

[Claims] In a magneto-optical pickup that obtains an information signal by using polarization information of return light from a magneto-optical recording medium, an optical sensor is installed in an optical system between the recording medium and a photodetector that detects the return light from the recording medium. , a hologram having polarization characteristics that generates a light beam for detecting an information signal, and an error signal detection hologram generating a light beam for detecting an error signal of at least one of focusing and tracking; , a magneto-optical pickup characterized in that the error signal detection hologram is integrated by providing it on each end face of a transparent substrate.